Fluid transfer devices (e.g., pipette mechanisms) are used to transfer small volumes of fluid in many applications. The devices may range from simple glass tubes to more elaborate mechanical displacement devices. In either case, the devices operate by displacing air and a seal is used to hold the displaced air, which facilitates the liquid transfer. Traditional devices use displacement pistons with mechanical seals such as lip seals or o-rings to prevent the air from entering the displacement chamber. These seals can be run dry, and wear eventually causes the seal to leak air and degrades accuracy of the device.
Accordingly, there is a need for a sealed air displacement apparatus that substantially prevents air leakage and that is capable of running longer without wear or leakage.